Many embodiments in the present disclosure relate to implantable cardiac pulse generators (IPGs) generally, and more particularly to implantable cardioverters defibrillators (ICDs) and triple-chamber pacing devices configured to deliver cardiac resynchronization therapy (CRT).
Cardiac conduction defects and various co-morbidities of heart failure can confound the natural cardiac depolarization sequence so that upper and lower chambers fail to electrically conduct and mechanically contract during normal sinus rhythm (NSR) and/or without ventricular synchrony. In certain heart failure patients, the heart may become dilated, and the conduction and depolarization sequences of the heart chambers may, for example, exhibit inter-and/or intra-atrial conduction defects (IACD), left bundle branch block (LBBB), right bundle branch block (RBBB), and inter-ventricular conduction defects (IVCD) and the like. In patients suffering from each or a combination of such conduction defects, a lack of synchrony and/or complementary blood flow among the chambers can diminish cardiac output and impair perfusion of the organs of tissues of the patient. In addition, spontaneous depolarizations originating within the right atrium, left atrium (RA, LA), the right ventricle (RV), and/or the left ventricle (LV) can arise from diverse locations (e.g., at one or more ectopic foci) thus disturbing the natural activation sequence. Further, significant conduction disturbances between the RA and LA can result in atrial flutter or fibrillation (e.g., which can significantly impair LV filling due to the arrthymia within the LA).
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia conditions could be overcome by applying pacing pulses at multiple electrode sites positioned in or about a single or multiple chambers of a heart in synchrony with a depolarization that is sensed at one of multiple electrode sites. It is believed that cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy and heart failure.
For patients with dual chamber or triple chamber implantable devices appropriate timing between the RA and RV and the LA and LV is beneficial to achieve optimal hemodynamics. One consideration for selecting the appropriate timing is the time relationship between right and left atrial contraction. In current implantable systems, RA contraction can be determined from the RA electrical depolarization sensed from one or more electrodes coupled to a lead disposed in communication with the RA. In these systems, there is no good way to determine the electrical depolarization and mechanical contraction timing of the LA. This is because the bipolar RA electrogram (EGM) mostly represents the localized electrical activities (e.g., near field) in the RA and not the LA. The unipolar RA EGM from the RA tip also suffers from the similar limitation as the tip signal is dominated by the local myocardium around the tip electrode.
In current practice, clinicians have used Doppler echocardiography to guide A-V and/or V-V optimization in patients with CRT. They are typically done a month or so after implant. Sometimes, clinicians would only selectively perform so-called echo-guided optimization in non-responder patients (i.e., patients that fail to improve hemodynamics in response to CRT delivery) due to increased number of device implants as well as difficulties in scheduling visits to qualified clinicians such as an electrophysiologist or an echo technician. However, it is unknown whether the A-V delay interval or inter-ventricular (V-V) interval, if any, selected during an echo-guided optimization performed when the patient is supine and resting are the same as when the patient is ambulatory and active. Similarly, as the patient's disease state evolves, for example, due to an acute heart failure decompensation event or because of deleterious remodeling that occurs in the progression of heart failure or otherwise during the course of heart failure treatment and therapy, it is foreseeable that the A-V and/or V-V timing would change as well and thus benefit from a closed loop method and apparatus for adapting to same.